Altera Stratix GX Transceiver - Manual (Page 52)

3–6 Altera Corporation
Stratix GX Transceiver User Guide January 2005
Basic Mode Receiver Architecture
Figure 3–5 shows an example of how the word aligner signals interact in
10-bit alignment mode. For this example, a /K28.5/
(10'b0011111010)
is specified as the comma. Because rx_enacdet is
held high at time n, alignment occurs whenever a comma exists in the
pattern. The rx_patterndetect signal is asserted for one clock cycle to
signify that the pattern exists on the re-aligned boundary. The
rx_syncstatus
signal is also asserted for one clock cycle to signify that
the boundary has been synchronized.
Figure 3–5. Example of How the Word Aligner Symbols Interact in 10-Bit Manual Alignment Mode
At time n+1 the rx_enacdet signal is deasserted, which instructs the
word aligner to lock the current word boundary. The comma is detected
at time n+2, but it exists on a different boundary than the current locked
boundary. Because the bit orientation of the Stratix GX device is LSB to
MSB, it follows, from the waveform, that the comma exists across time
n+2 and n+3. In this condition, the rx_patterndetect signal remains
low because the comma does not exist on the current word boundary, but
the rx_syncstatus signal is asserted for one clock cycle to signify a
resynchronization condition. This means that the comma has been
detected, but across another word boundary. The logic of the design
determines whether to assert the rx_enacdet signal to re-initiate the
word alignment process. At time n+5 the rx_patterndetect signal is
asserted for one clock cycle to signify that the comma has been detected
on the current word boundary.
Manual 16-bit Alignment Mode
You can enable the 16-bit alignment mode if the data widths are 8-bits or
16-bits. This mode is similar to the manual A1A2 SONET alignment
mode, except that the rx_a1a2size[] and rx_a1a2sizeout[]
signals are not available.
rx_recovclockout
rx_enacdet
rx_patterndetect
rx_syncstatus
rx_word_align_out 111110000 0101111100 111110000 111110000 1000000101 0101111100 1111001010
n n+1 n+2 n+3 n+4 n+5